$-\dfrac{9}{4} + \dfrac{4}{2} = {?}$
Solution: $ = - {\dfrac{9 \times 1}{4 \times 1}} + {\dfrac{4 \times 2}{2 \times 2}} $ $ = - {\dfrac{9}{4}} + {\dfrac{8}{4}} $ $ = - \dfrac{{9} + {8}}{4} $ $ = -\dfrac{1}{4}$